// https://www.gsma.com/about-us/wp-content/uploads/2014/12/eea3eia3zucv16.pdf
use std::array;

use base64::engine::{general_purpose::STANDARD, Engine};

const S0: [u8; 256] = [
    0x3e, 0x72, 0x5b, 0x47, 0xca, 0xe0, 0x00, 0x33, 0x04, 0xd1, 0x54, 0x98, 0x09, 0xb9, 0x6d, 0xcb,
    0x7b, 0x1b, 0xf9, 0x32, 0xaf, 0x9d, 0x6a, 0xa5, 0xb8, 0x2d, 0xfc, 0x1d, 0x08, 0x53, 0x03, 0x90,
    0x4d, 0x4e, 0x84, 0x99, 0xe4, 0xce, 0xd9, 0x91, 0xdd, 0xb6, 0x85, 0x48, 0x8b, 0x29, 0x6e, 0xac,
    0xcd, 0xc1, 0xf8, 0x1e, 0x73, 0x43, 0x69, 0xc6, 0xb5, 0xbd, 0xfd, 0x39, 0x63, 0x20, 0xd4, 0x38,
    0x76, 0x7d, 0xb2, 0xa7, 0xcf, 0xed, 0x57, 0xc5, 0xf3, 0x2c, 0xbb, 0x14, 0x21, 0x06, 0x55, 0x9b,
    0xe3, 0xef, 0x5e, 0x31, 0x4f, 0x7f, 0x5a, 0xa4, 0x0d, 0x82, 0x51, 0x49, 0x5f, 0xba, 0x58, 0x1c,
    0x4a, 0x16, 0xd5, 0x17, 0xa8, 0x92, 0x24, 0x1f, 0x8c, 0xff, 0xd8, 0xae, 0x2e, 0x01, 0xd3, 0xad,
    0x3b, 0x4b, 0xda, 0x46, 0xeb, 0xc9, 0xde, 0x9a, 0x8f, 0x87, 0xd7, 0x3a, 0x80, 0x6f, 0x2f, 0xc8,
    0xb1, 0xb4, 0x37, 0xf7, 0x0a, 0x22, 0x13, 0x28, 0x7c, 0xcc, 0x3c, 0x89, 0xc7, 0xc3, 0x96, 0x56,
    0x07, 0xbf, 0x7e, 0xf0, 0x0b, 0x2b, 0x97, 0x52, 0x35, 0x41, 0x79, 0x61, 0xa6, 0x4c, 0x10, 0xfe,
    0xbc, 0x26, 0x95, 0x88, 0x8a, 0xb0, 0xa3, 0xfb, 0xc0, 0x18, 0x94, 0xf2, 0xe1, 0xe5, 0xe9, 0x5d,
    0xd0, 0xdc, 0x11, 0x66, 0x64, 0x5c, 0xec, 0x59, 0x42, 0x75, 0x12, 0xf5, 0x74, 0x9c, 0xaa, 0x23,
    0x0e, 0x86, 0xab, 0xbe, 0x2a, 0x02, 0xe7, 0x67, 0xe6, 0x44, 0xa2, 0x6c, 0xc2, 0x93, 0x9f, 0xf1,
    0xf6, 0xfa, 0x36, 0xd2, 0x50, 0x68, 0x9e, 0x62, 0x71, 0x15, 0x3d, 0xd6, 0x40, 0xc4, 0xe2, 0x0f,
    0x8e, 0x83, 0x77, 0x6b, 0x25, 0x05, 0x3f, 0x0c, 0x30, 0xea, 0x70, 0xb7, 0xa1, 0xe8, 0xa9, 0x65,
    0x8d, 0x27, 0x1a, 0xdb, 0x81, 0xb3, 0xa0, 0xf4, 0x45, 0x7a, 0x19, 0xdf, 0xee, 0x78, 0x34, 0x60,
];
const S1: [u8; 256] = [
    0x55, 0xc2, 0x63, 0x71, 0x3b, 0xc8, 0x47, 0x86, 0x9f, 0x3c, 0xda, 0x5b, 0x29, 0xaa, 0xfd, 0x77,
    0x8c, 0xc5, 0x94, 0x0c, 0xa6, 0x1a, 0x13, 0x00, 0xe3, 0xa8, 0x16, 0x72, 0x40, 0xf9, 0xf8, 0x42,
    0x44, 0x26, 0x68, 0x96, 0x81, 0xd9, 0x45, 0x3e, 0x10, 0x76, 0xc6, 0xa7, 0x8b, 0x39, 0x43, 0xe1,
    0x3a, 0xb5, 0x56, 0x2a, 0xc0, 0x6d, 0xb3, 0x05, 0x22, 0x66, 0xbf, 0xdc, 0x0b, 0xfa, 0x62, 0x48,
    0xdd, 0x20, 0x11, 0x06, 0x36, 0xc9, 0xc1, 0xcf, 0xf6, 0x27, 0x52, 0xbb, 0x69, 0xf5, 0xd4, 0x87,
    0x7f, 0x84, 0x4c, 0xd2, 0x9c, 0x57, 0xa4, 0xbc, 0x4f, 0x9a, 0xdf, 0xfe, 0xd6, 0x8d, 0x7a, 0xeb,
    0x2b, 0x53, 0xd8, 0x5c, 0xa1, 0x14, 0x17, 0xfb, 0x23, 0xd5, 0x7d, 0x30, 0x67, 0x73, 0x08, 0x09,
    0xee, 0xb7, 0x70, 0x3f, 0x61, 0xb2, 0x19, 0x8e, 0x4e, 0xe5, 0x4b, 0x93, 0x8f, 0x5d, 0xdb, 0xa9,
    0xad, 0xf1, 0xae, 0x2e, 0xcb, 0x0d, 0xfc, 0xf4, 0x2d, 0x46, 0x6e, 0x1d, 0x97, 0xe8, 0xd1, 0xe9,
    0x4d, 0x37, 0xa5, 0x75, 0x5e, 0x83, 0x9e, 0xab, 0x82, 0x9d, 0xb9, 0x1c, 0xe0, 0xcd, 0x49, 0x89,
    0x01, 0xb6, 0xbd, 0x58, 0x24, 0xa2, 0x5f, 0x38, 0x78, 0x99, 0x15, 0x90, 0x50, 0xb8, 0x95, 0xe4,
    0xd0, 0x91, 0xc7, 0xce, 0xed, 0x0f, 0xb4, 0x6f, 0xa0, 0xcc, 0xf0, 0x02, 0x4a, 0x79, 0xc3, 0xde,
    0xa3, 0xef, 0xea, 0x51, 0xe6, 0x6b, 0x18, 0xec, 0x1b, 0x2c, 0x80, 0xf7, 0x74, 0xe7, 0xff, 0x21,
    0x5a, 0x6a, 0x54, 0x1e, 0x41, 0x31, 0x92, 0x35, 0xc4, 0x33, 0x07, 0x0a, 0xba, 0x7e, 0x0e, 0x34,
    0x88, 0xb1, 0x98, 0x7c, 0xf3, 0x3d, 0x60, 0x6c, 0x7b, 0xca, 0xd3, 0x1f, 0x32, 0x65, 0x04, 0x28,
    0x64, 0xbe, 0x85, 0x9b, 0x2f, 0x59, 0x8a, 0xd7, 0xb0, 0x25, 0xac, 0xaf, 0x12, 0x03, 0xe2, 0xf2,
];

const EK_D: [u16; 16] = [
    0x44D7, 0x26BC, 0x626B, 0x135E, 0x5789, 0x35E2, 0x7135, 0x09AF, 0x4D78, 0x2F13, 0x6BC4, 0x1AF1,
    0x5E26, 0x3C4D, 0x789A, 0x47AC,
];

const POLY: u32 = 0x7FFFFFFF;

fn mul_pow_2_mod(x: u32, y: u32) -> u32 {
    (x.wrapping_shl(y) | (x >> (31 - y))) & POLY
}
fn add_mod(x: u32, y: u32) -> u32 {
    let z = x + y;
    (z & POLY) + (z >> 31)
}

fn l1(x: u32) -> u32 {
    x ^ x.rotate_left(2) ^ x.rotate_left(10) ^ x.rotate_left(18) ^ x.rotate_left(24)
}
fn l2(x: u32) -> u32 {
    x ^ x.rotate_left(8) ^ x.rotate_left(14) ^ x.rotate_left(22) ^ x.rotate_left(30)
}

fn sbox(x: u32) -> u32 {
    let [a, b, c, d] = x.to_be_bytes();
    u32::from_be_bytes([
        S0[a as usize],
        S1[b as usize],
        S0[c as usize],
        S1[d as usize],
    ])
}

struct Cipher {
    lfsr: [u32; 16],
    f_r1: u32,
    f_r2: u32,
    brc_x: [u32; 4],
}
impl Cipher {
    fn new(key: &[u8], iv: &[u8]) -> Self {
        assert_eq!(key.len(), 16);
        assert_eq!(iv.len(), 16);
        let mut this = Self {
            lfsr: array::from_fn(|i| {
                ((key[i] as u32) << 23) | ((EK_D[i] as u32) << 8) | iv[i] as u32
            }),
            f_r1: 0,
            f_r2: 0,
            brc_x: [0; 4],
        };
        for _ in 0..32 {
            this.bit_reorganization();
            let w = this.f();
            this.update_lsfr(w >> 1);
        }

        this.next();
        this
    }

    fn bit_reorganization(&mut self) {
        self.brc_x[0] = ((self.lfsr[15] & 0x7FFF8000) << 1) | (self.lfsr[14] & 0xFFFF);
        self.brc_x[1] = ((self.lfsr[11] & 0xFFFF) << 16) | (self.lfsr[9] >> 15);
        self.brc_x[2] = ((self.lfsr[7] & 0xFFFF) << 16) | (self.lfsr[5] >> 15);
        self.brc_x[3] = ((self.lfsr[2] & 0xFFFF) << 16) | (self.lfsr[0] >> 15);
    }

    fn feed(&mut self, s16: u32) {
        self.lfsr.copy_within(1..16, 0);
        self.lfsr[15] = s16;
    }

    // lsfr_init_mode(u) -> update_lsfr(u)
    // lsfr_work_mode() -> update_lsfr(0)
    fn update_lsfr(&mut self, u: u32) {
        let mut v = add_mod(self.lfsr[0], u);
        v = add_mod(v, mul_pow_2_mod(self.lfsr[0], 8));
        v = add_mod(v, mul_pow_2_mod(self.lfsr[4], 20));
        v = add_mod(v, mul_pow_2_mod(self.lfsr[10], 21));
        v = add_mod(v, mul_pow_2_mod(self.lfsr[13], 17));
        v = add_mod(v, mul_pow_2_mod(self.lfsr[15], 15));
        self.feed(v);
    }

    fn f(&mut self) -> u32 {
        let w = (self.brc_x[0] ^ self.f_r1).wrapping_add(self.f_r2);
        let w1 = self.f_r1.wrapping_add(self.brc_x[1]);
        let w2 = self.f_r2 ^ self.brc_x[2];
        self.f_r1 = sbox(l1(w1.wrapping_shl(16) | (w2 >> 16)));
        self.f_r2 = sbox(l2(w2.wrapping_shl(16) | (w1 >> 16)));
        w
    }
}

impl Iterator for Cipher {
    type Item = u32;

    fn next(&mut self) -> Option<Self::Item> {
        self.bit_reorganization();
        let result = self.f() ^ self.brc_x[3];
        self.update_lsfr(0);
        Some(result)
    }
}

pub fn encryption(input: String) -> String {
    let cipher = Cipher::new(
        b"\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00",
        b"\x01\x01\x01\x01\x01\x01\x01\x01\x01\x01\x01\x01\x01\x01\x01\x01",
    );
    let mut bytes = input.as_bytes().to_vec();

    // PKCS#7 padding
    let rem = 4 - bytes.len() % 4;
    bytes.resize(bytes.len() + rem, rem as u8);

    for (chunk, keystream) in bytes.chunks_exact_mut(4).zip(cipher) {
        let mut x = u32::from_be_bytes([chunk[0], chunk[1], chunk[2], chunk[3]]);
        x ^= keystream;
        chunk.copy_from_slice(&x.to_be_bytes());
    }
    STANDARD.encode(&bytes)
}
